Finned heat exchanger



April 30, 1968 CANTELOUBE ET AL 3,380,518

FINNED HEAT EXCHANGER 2 Sheets-Sheet 1 Filed Feb. 15. 1966 & i3 U MU U KI. EEB W EE. .rgwmi iwlmw Tu 3 m g in Axvoes' (AA/2220065 /740 TAVERIVAApril 1968 A. CANTELOUBE IY-ZT AL 3,380,518

FINNED HEAT EXCHANGER 2 Sheets-Sheet 2 Filed Feb. 15. 1966 Ana/Wakes IAva/e: ('fl/VIZLOUIE lnaa f rmer/v United States Patent 3,380,518 FINNEDHEAT EXCHANGER Andr Canteloube, Ave. de Bretteville, Neuilly-sur- Seine,France, and Italo Taverna, 80 Blvd. de Valmy, Colombes, France FiledFeb. 15, 1966, Ser. No. 527,714 Claims priority, application France,Feb. 26, 1965,

7,159, Patent 1,434,385 3 Claims. (Cl. 165171) ABSTRACT OF THEDISCLOSURE A finned heat exchanger comprises a plate carrying a sinuoustube, and fins stamped from the material of the plate between andperpendicular to the lengths of the tube. The stamped fins are archedbridges extending alternately from opposite sides of the plates andhaving between at least some of them flat fins comprised by re mainingportions of the plate. The bridges extend outwardly from the plane ofthe plate farther than the tubes. The flat fins between the bridge-typefins may be at an acute angle to the plate.

This invention relates to a finned heat exchanger of improved design,useful mainly as a condenser or evaporator in cooling and refrigeratingsystems.

Many different types of heat exchange apparatus already exist in whichan internal fluid circulating within a tube system transfers heat byeither natural or forced convection to an externally flowing gas. Heatexchangers of this type usually have the shape of a plate which haseither a plane or, more often, a developable surface; and the process ofconvective heat transfer is improved by the provision of fins which arecut-out from the metal of the plate.

In a first type of heat exchanger, the tube system is secured to theplate by welding, bonding or mechanical assembly of a coiled tube. In asecond type of heat exchanger, the tube system is formed by expansionwithin the thickness of the plate which is in that case made up of twosheets having deformations which correspond to the fluid-circulationsystem and which are assembled by a' number of different methods outsidethe expanded sections, this arrangement being known as an integratedtube system.

Another known method of construction of heat exchangers of theintegrated tube type consists in forming fins by die-stamping, cuttingand folding portions of the tube plate which are located between thetube sections, wherein the rectilineal fins formed extend slantwise withrespect to the plane of the plate.

A further known method of construction which is employed in a heatexchanger of the built-up sheet or integrated tube type consists indeforming the sheet by cutting-out and stamping in such a manner as toform between two lengths of the sinuous tube having an undulated path asuccession of transverse undulations which are similar .to sinusoids andproject alternately on each side of the plane of the plate. Thedirection of these undulations is reversed from one line to the next.

There is thus obtained a plate having a fluted surface in which isformed a series of ducts for the flow of air, said ducts extendingparallel to the rectilineal lengths of the tube.

Heat exchangers of this type are characterized by an improved heattransfer coefficient but nevertheless do not derive the maximum thermaladvantage from the surfaces of the fins "for the following reasons:

In the first place, the cutting of multiple undulations sets alimitation on the amplitude of the undulation or wave, with the resultthat optimum permeability of the surface to gas flow is not afforded. Inthe second place, since each fin is made up of a number of consecutivehalfwaves, the central portions of the fins which are located betweentwo tube-lengths are at a distance from these latter which is greatcompared with the thickness of the sheet. The temperature gradientbetween these portions of the fins and the surrounding atmosphere istherefor low as a result of limited transmission of heat flow throughthe sheet. As a consequence, heat transfer is reduced.

It has also been proved by experience that heat exchangers of the typereferred to above do not provide sufficient mechanical ruggednessinasmuch as the fins are prevented by their small amplitude fromcreating a protection zone which extends a sufficient distance away fromthe tubes. Moreover, the fins afford low resistance to compressivestresses which are normal to the plane of the plate.

The different systems of fins proposed in devices of the prior art areusually intended to produce uniform flow of surrounding gas layers bycausing these latter to pass through the mid-plane of the heat exchangerapparatus in a substantially laminar flow pattern.

The present invention is based on the discovery that the thermalefficiency of heat exchangers of the type discussed in the foregoing canbe improved to a very appreciable extent by means of fins designed toproduce a substantial modification in the air flow pattern. It istherefor one of the objects of the present invention to improve theefficiency of the finned heat exchangers.

A further advantage of the heat exchange structure in accordance withthe invention lies in the fact that it provides distinctly improvedmechanical strength. It is therefor another object of the invention toimprove the mechanical strength of the finned heat exchangers.

In accordance with the invention, the'heat exchanger such as a condenseror evaporator for use in a cooling or refrigerating apparatus comprisesa sinuous tube in heatconducting relation with a plate provided withfins which are cut-out and cambered so as to project from said platebetween the lengths of said sinuous tube and in staggered verticalrelation on said plate, and is chiefly characterized in that a firstgroup of fins is formed in a manner known per se by punched-out bridgeswhich project either on one side or on the other side of the plane ofthe plate whilst a second group which also extends between thetube-lengths consists of fins which are substantially flat.

The second group of fins is primarily intended to deflect the airstreams which are established by convection within the chimneys whichare formed parallel to the tubelengths and on each side of the plate bythe bridge-type fins. It is thus possible to transform the gas-flow froma laminar to a turbulent flow pattern. The flat fins have the additionalfunction of spacer members between the tubelengths, therebystrengthening the plate.

As a preferred feature, said flat fins are generally inclined to themid-plane of the tube if it is desired to increase the turbulence of thegas streamlines which move by convection along the heat exchanger.

The complete heat exchanger unit can be obtained by reproducing aparticular configuration of a group of 3, 4 or n fins according to apredetermined periodic law. In all cases, the heat exchange unit can beobtained by cutting out and stamping in opposite directions a flatmetallic sheet which is either plain or which preferably comprises anintegrated tube system.

When the heat exchanger is of the integrated tube type, the improvementscontemplated by the invention result in additional technical advantageswhich will be explained hereinafter.

Further characteristic features and objects of the invention will becomeapparent from the description which now follows:

In the accompanying drawings, which are given by way of non-limitativeexample,

FIG. 1 is a partial view in elevation of a particular embodiment ofcooling condenser in accordance with the invention, designed on theintegrated tube principle;

FIG. 2 is a partial view in perspective of the bottom left-hand portionof the above-mentioned condenser;

FIG. 3 is a transverse sectional view along the line III- III of FIG. 1;

FIG. 4 is a transverse sectional view of the fins taken along thetransverse plane IVIV of FIG. 1;

FIGS. 5 to 11 are partial transverse sectional views of the fins whichare similar to FIG. 4 and which relate to various alternativeembodiments.

In the particular construction of the invention which is shown in FIGS.1 to 4, the heat exchanger is a cooling condenser. Said condensercomprises an integrated tube system consisting of a sinuous orsnake-like tube 1 which is formed by expansion in accordance with aknown technique from a double-walled plate 2 of aluminum oraluminum-base alloy. The end sections of the tube 1 are provided withunions 3 for connecting purposes.

Provision is made between the consecutive rectilineal and paralleltube-length 1a, 1b of the heat exchanger for rows of transverse finswhich are arranged in two groups.

The fins of the first group are formed by means of punched-out strips orbridges 11, which project respectively on each side of the plane of theplate 2. The longitudinal edges such as 12 and 13 of each bridge areparallel to each other. The ends of the bridges are located in proximityto the adjacent tube-lengths 1a and 1b of the tube 1 and each bridgeextends substantially at right angles to said tube-lengths. Theperimeter of each bridge corresponds to an isosceles trapezium (as shownin FIG. 3), the large base of which is located in the plane of the plate2. According to another characteristic feature of the invention, stepsare preferably taken to ensure that height H of the bridges 11 (or 15)relatively to the plane of the plate 2 is greater than the height h ordistance to which the tube-lengths 1a, 1b of the tube 1 project fromsaid plane (as shown in FIG. 3).

The fins 14 of the second group are flat and extend in the plane of theplate 2 from one tube-length 1a to the adjacent tube-length 1b. Inaddition, the fiat fins 14 are located between two successive bridgefins 11, 15 of opposite convexity.

The combined assembly of fins of plate 2 thus corresponds to therepetition of a unitary pattern in which each fin 14 located in theplane of the plate 2 is in adjacent relation with two bridges 11 and 15which extend transversely in opposite directions relatively of the planeof the plate 2. Under these conditions, looking on the condenser in theposition shown in FIG. 2, it can be seen that the fins 11 are raised andthe fins 15 are concave. In the embodiment considered, the fins 11 and15 have a prismatic surface, the generator-lines of which are parallelto the plane of the plate 2, the two end faces of said surface beingoriented slantwise with respect to the plane considered.

The complete assembly of fins can be formed by cutting-out the flatportion of the plate 2 which is located between the tube lengths 1a, 1b.The bridges 11 and 15 are formed by means of die-stamping punches whichproduce elongation of the fins without resulting in fracture of themetal.

In addition to the fins which are formed between the tube-lengthsconsidered, the plate 2 of the heat exchanger is preferably providedwith complementary fins 16 located beyond the path of the sinuous tube1.

The structure as thus formed has a high thermal transparency and ispreferably placed in such a manner that the tube-lengths 1a, 1b of thetube 1 are vertical or, better still, at an angle of 4 to 8 with respectto the vertical, in which position the overall thermal efiiciency of thecondenser is particularly high.

In this manner, it has been possible to obtain a heat transfercoefficient equal to 10.95 c.g.s. Whereas a condenser of conventionaltype and equivalent size having a sinuous tube 1 which is bonded to alouvered sheet gives a value of 5.05 c.g.s. under similar operatingconditions.

This technical improvement can be explained, although it will beunderstood that the invention is not dependent on this explanation, bypointing out that the structure which is contemplated by the inventionproduces a circulation of air by convection according to a turbulentflow pattern. The punched-out strips or bridges 11 and 15 are in contactwith relatively thick layers of gas which flow on each side of themid-plane of the heat exchanger. Turbulent flow conditions are improvedby the flat fins 14 since these latter counteract the chimney effectwhich can be created by the projecting fins 11, 15.

Inasmuch as each bridge 11 or 15 also extends between two adjacenttube-lengths 1a, 1b of the tube 1, the temperature gradient between thecentral portion of the bridge and the end roots of the bridge is ofmaximum value, thereby improving the heat transfer processes. The factthat the fins perimeter is trapezoidal instead of circular makes itpossible for the ends of the bridges to be raised from the plane of theplate 2 to a greater extent, with the result that inter-fin air flow ismore effective.

Since the bridges 11 and 15 are formed by die-stamping, the slopingsections of these latter are subjected during the stamping operation toelongation which reduces their thickness. By virtue of thiscircumstance, the invention is of particular interest in integrated tubeexchangers, in which the initial thickness of the sheet metal employedis greater than the thickness required for maximum heat transferperformance of the fins. The thinning of the fins which results from thedie-stamping operation makes it possible to restore the fins to optimumconditions of thickness.

From the mechanical standpoint, the structure which is contemplated forthe fins also provides substantial advantages. In fact, on the one hand,the height H to which the bridges 11 and 15 project with respect to thetubelengths 1a, 1b ensures mechanical protection of these latter.Inasmuch as the bridges 11 and 15 are in adjacent relation to a flat fin14 which serves as a spacer member, the compressive strength of the heatexchanger is particularly high in view of the fact that, in the event ofcompressive stress exerted on the bridges 1.1 and 15, said bridges tendto buckle and not to fold. The structure as herein described istherefore endowed wit-h high strength.

By virture of the above-mentioned property which is combined with theprotection given to the tube-lengths 1a, 1b, condensers fabricated ofaluminum sheet can be mounted directly and without danger on the rear ofrefrigerators without requiring any form of protection.

In the version of FIG. 5, the turbulent-flow effect is increased by thearrangement of bridges 19, 21 or 22, 23 which are located at differentdistances from the plane of the plate 2. It is apparent that, in thismanner, the upfiowing air streams which pass between the end bridges 21(or 23) and the flat central fins 20 are deflected by the intermediatebridges 19 (or 22) which are located at a medium distance from theplate. Under these conditions, there is no passageway for the freeconduction of surrounding gas.

In the embodiment which is shown in FIG. 6, the various bridges 41, 42,44, 45 which have different spacing are separated from each other by theflat fins 43.

The versions of FIGS. 7 and 8 are characterized in that they compriseflat fins 25 which are turned down by stamping in such a manner as topresent a certain inclination with respect to the plane of the plate 2,the center-line of said fins being located in this plane. Thisinclination is preferably comprised between 20 and 40. The fins 25 canhave a tendency to direct the deflected air streams towards the exterior(which is the case shown in FIG. 7) or towards a bridge 26 or 27 (asshown in FIG. 8).

The flat fins 25 can have contrary inclinations from one ,row to another(case of FIGS. 7 and 8) or, on the contrary, they can all be parallelwith each other, which is the case of the fins 28 shown in FIG. 9. Thislast-mentioned armrangement tends to establish a general displacement ofthe gas flow from one side to the other of the heat exchanger. Such adisplacement is increased in the case of FIG. in which the fiat fins 29and the bridge-type fins 30 and 31 are turned down in the samedirection.

Finally, the combined arrangement of the inclined fins 32 andbridge-type fins 33, 34 as progressively spaced is shown in FIG. 11.

As will be readily understood, it would not constitute a departure fromthe scope of the invention to construct heat exchangers by making use ofa plain finned sheet on which the sinuous tube is fixed in known mannereither by welding or bonding, the locations for the lengths of said tubebeing reserved between the rows of fins.

We claim:

1. A heat exchanger comprising a plate, a sinuous tube for circulationof a heat-exchange fluid borne by said plate in heat-exchange relationtherewith, said sinuous tube having several tube lengths, a plurality offins comprising arched bridges punched out from said plate and extendingsome on one side and some on the other side of the plate, saidbridge-type fins extending away from the plate a greater distance thanthe tube so that the bridge-type fins protect the tube from damage andpartake more fully in convective heat transfer, and further finscomprising substantially flat strips disposed between at least some ofsaid bridge-type fins at acute angles with respect to the plate.

2. A heat exchanger as claimed in claim 1, some of said further finsbeing disposed at acute angles of a given sense to the plate and othersof said further fins being disposed at acute angles of the oppositesense to the plate.

3. A natural convection heat exchanger comprising a substantiallyvertical plane plate, a sinuous tube for circulation of a heat exchangefiuid borne by said plate in heat-exchange relation therewith, saidsinuous tube having several parallel and substantially vertical tubelengths having their axes in the plane of said plate and a plurality offins comprising arched bridges punched out from said plate, each finjoining two successive tube lengths and extending some on one side andsome on the other side of the plate, and further fins comprisingsubstantially flat strips disposed between at least some of saidbridge-type fins, the lengthwise extent of all fins being horizontallydisposed, said heat exchanger being of the integrated tube type, saidarched bridge-type fins having a substantially trapezoidal contourcomprising two sloping sections and wherein the thickness of saidsloping sections is smaller than the thickness of said exchanger plate,said bridge-type fins extending away from the plate a greater distancethan the tube so that the bridge-type fins protect the tube from damageand partake more fully in convective heat transfer.

References Cited UNITED STATES PATENTS 3,135,320 6/1964 Forgo -1513,224,503 12/1965 Konanz 165l71 3,265,127 8/1966 Nickol et a1. 1651523,273,637 9/ 1966 Pa-uls 165171 FOREIGN PATENTS 1,191,954 4/1959 France.

1,212,813 10/1959 France.

ROBERT A. OLEARY, Primary Examiner.

M. A. ANTONAKAS, Assistant Examiner.

